A variety of criteria have to be met for medical catheters to be serviceable. Some of these requirements are at least somewhat inconsistent with one another. For example, a catheter, in order to have the distal end follow the proximal end, has to be made of material of a rigidity to convey torque from the proximal to the distal end. Unfortunately, any material sufficiently rigid to convey the torque may be too rigid to maneuver in some areas in the body into which insertion is required. The tip has to be softer than the body of the catheter.
Prior art attempts to overcome this problem include gluing a tip of relatively soft material onto the distal end of the catheter. This approach has proven to be hazardous, because the tips do come off, and are difficult to retrieve as they move in the body. Also, if such a tip reaches the heart, it most likely is fatal.
Another attempt is to make a catheter with a relatively rigid inner layer and a relatively soft outer layer. The inner layer is removed from the distal end and the outer layer at the distal end is heated and drawn down to form a soft tip. This approach not only is relatively expensive, but reduces the thickness of the catheter wall at the tip, running the risk of rupture and sacrificing torque. Further, lumen diameter is difficult to maintain constant.